COVID-19 Vaccine Breakthrough Infections and Compliance to Non-Pharmaceutical Public Health Interventions: A Nested Case-Control Study

Vaccination against SARS-CoV-2 was a leading strategy to change the course of the COVID-19 pandemic worldwide. Nonetheless, some people still contracted the infection. Causes for breakthrough infections post vaccination with atleast 1 dose, can be many such as age, time since vaccination, level of immunity at the moment of exposure, variant to which the individual was exposed, and compliance to non- pharmaceutical interventions. Out of the 2549 SARS CoV-2 infections, majority (42.6%) got infected between 31-90 days after receiving the second dose, 22% were infected within 14 days of receiving the second dose, and 12.3% were infected before receiving the second dose while only 5% of the cases were infected after 3 months post-second dose. This retrospective nested case-control study was conducted to examine whether non-compliance to non-pharmaceutical public health interventions can explain the SARS-CoV-2 breakthrough infection among the vaccinated population. Irrespective of the vaccination status, majority of the 4456, adhered to avoiding social-gatherings (76.9%), avoided physical-contacts (59.5%), wearing facemasks (59.4%), regular hand-hygiene (53.9%) and social-distancing (49.5%). People who adhered to getting vaccinated against the infection, adhered to the precautionary measures mandated to prevent spread of infection, though may not always. Our study found significant association between vaccination status and compliance to the nonpharmaceutical public health interventions as well as between compliance to the non-pharmaceutical public health interventions and breakthrough SARS-CoV-2 infections. A short-term public health response to an increase in severe breakthrough infections, would be to reimpose non-pharmaceutical preventive measures to slow the transmission while a medium-term solution would be to develop newer vaccine formulations or identify newer non-pharmaceutical interventions.